Courtesy PhotoFrom left, Meryl Streep, Steve Martin, Alec Baldwin and Lake Bell are shown in a scene from "It's Complicated."Writer-director Nancy Meyers is one of the best friends an actress can have. Not only does she know how to craft substantial parts and write witty lines, she also realizes women don't automatically lose their appeal once they reach that much-murmured-about "certain age." So in "It's Complicated," Meyers unleashes a new sex kitten: Her name is Meryl Streep.

If it's difficult to picture Streep, once far more renowned for her talent for suffering than for her sultriness, as prime date-bait take a look at how she peels back the lovely layers of Jane Adler, a successful Santa Barbara bakery owner and mother of three grown children who has never fully recovered from losing her husband, Jake (Alec Baldwin), to a tattooed, hip-swinging twentysomething.

When Meyers introduces us to Jane, she's in mid-laugh at a party, doing her best to put on a happy face while Jake stands nearby. Meyers and Streep know how women like this behave in such situations: They laugh too loudly, wear smiles dripping with desperation and cling to their glasses of white wine as if they were life preservers in a stormy sea.

Although Jane is the type who leads a perfectly coordinated life -- you can see that in the way her violet eyeglasses match her violet blouse and dark purple boots -- she's not entirely satisfied with her post-divorce life. So after she and Jake rekindle that old flame during a night of partying in Manhattan, Jane is simultaneously ashamed of herself and secretly thrilled. After all, what sweeter triumph could an abandoned woman score than to win back the man who once walked away from her?

But Meyers raises the stakes. Just as relations are heating up again for Jane and Jake, along comes Adam (Steve Martin), the amiable architect who is designing an extension on Jane's home. He's clearly infatuated with her, which leaves Jane at a romantic crossroads: Should she stick with the tried-and-true (even though he has a record of being untrue) or make a fresh start with a promising new partner?

It's a situation a great many women would love to find themselves in, which is why "It's Complicated" will almost certainly connect with viewers who flocked to Meyers' 2003 Diane Keaton-driven hit "Something's Gotta Give." Wacky, swiftly paced and set to a samba-flavored score by composer Hans Zimmer and guitarist Heitor Pereira, this is the sort of movie that in an earlier era would have been called "frothy" or "a romp." The same could be said of Meyers' earlier films, such as "What Women Want" and "The Holiday," although "It's Complicated" is smoother and snappier than either of those.

Streep sparkles as Jane slowly gives in to her lustier side, yet she insists on moving past Jane's sensual reawakening to give us revealing glimpses of someone who looks like a success but doesn't always feel like a winner, especially as she faces the dreaded "empty nest" years. In one wonderful moment during her son's graduation ceremony, Jane segues from cheering and whistling excitedly to sobbing in a matter of seconds: Although it's funny, at the same time it's also a sharp bit of shorthand for Jane's precarious emotional state.

While Streep may be the ringmaster of "It's Complicated," Baldwin is definitely the big cat. Proudly showing off his paunchy physique and purring ridiculous come-on lines into Jane's ear, Jake is the epitome of the one-time heartthrob-gone-to-seed-in-the-suburbs, a man who thinks he can seduce his ex-wife by reminding her that "people in nursing homes who have plants live longer than the people without plants." Baldwin's line-readings combine sleaziness and sweetness for often hilarious results ("I looooove when you smell like butter!" he moans as he nuzzles Jane in her kitchen) and, even though Jake may leave much to be desired in terms of moral fiber, it's no mystery why Jane responds to him.

As the designated nice guy in the picture, Martin has less of a chance to show off his comic chops until relatively late in the game. Thankfully, when he's finally allowed to loosen up, first in a smashingly funny party scene and then in a late-night baking session with Jane, he's a delight. John Krasinski also earns big laughs as Jane's future son-in-law, who is quietly horrified by all that's going on around him. Meyers' screenplay is sprightly and clever, but it's her sensational cast that gives this bubbly comedy its effervescence.